This invention relates generally to the combination of an electric lamp and a safety coating for preventing broadcasting of glass shards upon the glass envelope of the lamp being broken, and more particularly relates to the combination of a composite safety coating and fluorescent lamps providing high light output and very high light output which fluorescent lamps are known in the art as HO and VHO fluorescent lamps; an example of such fluorescent lamp is the F96T12/CW/HO for 96", 11/2" diameter Cool White High Output Lamp sold by Sylvania.
A diagrammatical illustration of a HO or VHO fluorescent lamp is shown in FIG. 1. The HO or VHO fluorescent lamp is indicated by general numerical designation 10 and includes a glass envelope 12 and end caps 14 and 16 provided at each end of the glass envelope and sealingly connected thereto in a manner known to those skilled in the art. The HO or VHO lamp, in the manner known to those skilled in the art, contains means (not shown) for generating high light output or very high light output upon energization of the lamp. As is still further known to those skilled in the art, upon such energization, the lengths of the glass envelope adjacent the end caps 14 and 26, identified in FIG. 1 as L1--L1, are heated to a first temperature much higher than the second temperature to which the middle length of the glass envelope indicated by L2 is heated. For example, in one embodiment each of an HO and a VHO fluorescent lamp, the lengths L1--L1 of the glass envelope adjacent the end caps were heated, respectively, to approximately 216.degree. F. and 256.degree. F. while the middle portion L2 of the glass envelopes of the HO and VHO fluorescent lamps were heated, respectively, to approximately 85.degree.-90.degree. F. In the HO and VHO fluorescent lamps, the length L1 measured approximately 21/21/2 inches irrespective of the length L2 of the middle portion of the lamps.
It has been found that this substantial difference in temperatures between the lengths of glass envelope L1--L1 adjacent the end caps and the middle portion of the glass envelope presents a difficult problem in providing the HO and VHO fluorescent lamps with a safety coating which is both effective in preventing broadcasting of glass shards upon the glass envelope 12 being broken and economically feasible with the cost of presently available electric lamp coating materials. This is due, primarily, to the substantial difference in the cost of electric lamp coating material which is non-degradeable to the higher temperatures to which the glass envelope lengths L1--L1 are heated and the cost of lamp coating material which is non-degradeable to the temperature to which the middle portion L1 of the lamp is heated; the term non-degradeable to a temperature means the temperature to which the coating material may be heated over the expected life of the lamp without the coating material melting, yellowing, or otherwise deteriorating and diminishing the amount of light that may be transmitted therethrough.
It has been found that Teflon produced by E.I. DuPont de Nemours & Company, Inc. is a suitable coating material for coating the lengths L1--L1 adjacent to the end caps of HO or VHO fluorescent lamps as the temperature to which Teflon is non-degradeable is well above the temperatures to which the glass envelope lengths L1--L1 are heated. However, since the present cost of Teflon is approximately $7.50 per foot of lamp coating, coating the entire length of a 96 inch or 8 foot HO or VHO fluorescent lamp with Teflon becomes economically infeasible due to the prohibitive cost of approximately $56.25 per fluorescent lamp. Surlyn, another plastic made by DuPont, is a suitable coating material for coating the middle portion L1 of the HO or VHO fluorescent lamps since Surlyn is non-degradeable well above the temperature to which the glass envelope length L2 is heated and since the present cost of Surlyn is only approximately $0.16 per foot of lamp coating. However, as is known, Surlyn degrades ruinously if heated to the higher temperatures to which the lengths L1--L1 of the glass envelope adjacent the end caps of the HO and VHO are heated.
Accordingly, it has been discovered that a composite safety coating for HO and VHO fluorescent lamps which includes a first coating of the more expensive material non-degradeable to the higher temperature for coating the glass envelope lengths L1--L1, and a second coating of the less expensive material which is non-degradeable to the lower temperature for coating the middle portion L2 of the HO and VHO fluorescent lamps, is needed. Thus, it has been discovered that a possible solution to this coating problem is to coat the shorter glass envelope lengths L1--L1 with Teflon and to coat the longer middle portion L2 with Surlyn, but as is further known to those skilled in the art, Teflon is a slick plastic to which other plastics, such as Surlyn, will not adhere or bond.
The teachings of the prior art are not instructive with regard to providing such a composite safety coating for HO and VHO fluorescent lamps, as such prior art teachings relate to the provision of a safety coating of a single material for preventing broadcasting of glass shards. Typical of such single material prior art safety coatings, and their process of manufacture, are those disclosed in U.S. Pat. No. 3,602,759, patented Aug. 31, 1978, George S. Evans, inventor; U.S. Pat. No. 3,621,323, patented Nov. 16, 1971, Frank W. Thomas, inventor; and U.S. Pat. No. 4,506,189, patented Mar. 19, 1985, James D. Nolan and Axel T. Karlsson, inventors.
Accordingly, there exists a need for a composite safety coating for HO and VHO fluorescent lamps which is both effective in preventing broadcasting of glass shards upon the glass envelope being broken and which is economically feasible with the present cost of electric lamp coating materials.